The present invention relates to aluminous gels and to methods for their preparation.
Gels comprising alumina hydrate combined with various organic compounds are known in the prior art. However, such gels generally take the form of a white floc rather than a stable clear gel.
For example, in Tu U.S. Pat. No. 4,215,015 anionic polyacrylamide is added to a silica-alumina slurry gel. The polyacrylamide is said to react chemically with the silica-alumina gel framework, thereby contributing to pore structure of inorganic oxide material formed by drying and calcining the gel.
Several other references also disclose addition of various organic polymers to solutions in which hydrous gels are precipitated. Montgomery et al U.S. Pat. No. 3,417,028 claims addition to gels of polyvinyl alcohol, polyethylene glycols, polyethylene oxides, methyl celluloses, and polyacrylamides. Disclosures of other organic additives are contained in Magee et al U.S. Pat. Nos. 3,322,494; 3,325,247 and 3,361,526.
Koch et al U.S. Pat. No. 3,152,865 discloses a process for stabilizing alumina gel wherein a chelating organic component of 2-10 carbon atoms containing two or more carboxyl groups is added to an aluminum chloride solution to form a slurry from which alumina monohydrate gel is precipitated. Two suitable chelating agents are oxalic acid and tartaric acid. Addition of the chelating agent is claimed to stabilize the alumina monohydrate against conversion to other hydrate forms of alumina.
Although the references summarized above each use the term "gel," reaction conditions described therein are believed to result in formation of white flocs rather than transparent, stable monolithic gels.
As used herein, the term "monolithic gel" refers to a gelled mass characterized by substantially no separation of a liquid phase. The term "floc" refers to a combination or aggregation of suspended particles in such a way that they form small clumps or tufts. A monolithic gel made in accordance with the present invention is generally transparent or slightly opalescent whereas an alumina hydrate floc is generally white. The term "gel" is often used in the prior art to describe what is called a floc herein.
The expression "alumina hydrate" refers to Al.sub.2 O.sub.3.sup.. x H.sub.2 O, where x varies from 1 to 3. In other words, the water of the alumina hydrate varies from 15.0 to 34.6 percent by weight of the alumina hydrate, determined by calcination at 538.degree. C. (1000.degree. F.) for one hour.
It is a principal objective of the present invention to provide a method for preparing a stable monolithic gel comprising alumina hydrate combined with an organic material.
A related objective of the invention is to provide a novel, stable monolithic gel comprising alumina hydrate combined with an organic material.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification and claims.